NEWS & PRESS

The hunt for dark matter has taken another step forward thanks to new supercomputer simulations showing the evolution of our 'local Universe' from the Big Bang to the present day. Physicists at Durham University, UK, who are leading the research, say their simulations could improve understanding of dark matter, a mysterious substance believed to make up 85 per cent of the mass of the Universe. The results will be presented at the National Astronomy Meeting in Portsmouth on Thursday 26 June.

The visible galaxies in the Local Group simulation, shown in the lower right, only trace a tiny fraction of the vast number of dark matter halos, revealed in the upper left. Credit: John Helly, Till Sawala, James Trayford, Durham UniversityProfessor Carlos Frenk, Director of Durham University’s Institute for Computational Cosmology, said: "I've been losing sleep over this for the last 30 years. Dark matter is the key to everything we know about galaxies, but we still don’t know its exact nature. Understanding how galaxies formed holds the key to the dark matter mystery."

Scientists believe clumps of dark matter – or haloes – that emerged from the early Universe, trapped intergalactic gas and became the birthplaces of galaxies. Cosmological theory predicts that our own cosmic neighbourhood should be teeming with millions of small halos, but only a few dozen small galaxies have been observed around the Milky Way.

Prof. Frenk added: "We know there can't be a galaxy in every halo. The question is: why not?"

The Durham researchers believe their simulations answer this question, showing explicitly how and why millions of haloes around our galaxy and neighbouring Andromeda failed to produce galaxies and became barren worlds. They say the gas that would have made the galaxy was sterilized by the heat from the first stars that formed in the Universe and was prevented from cooling and turning into stars.

However, a few haloes managed to bypass this cosmic furnace by growing early and fast enough to hold on to their gas and eventually form galaxies.

Prof. Frenk, who will also receive the Royal Astronomical Society’s top award, the Gold Medal for Astronomy on the same day, added: "We have learned that most dark matter haloes are quite different from the 'chosen few' that are lit up by starlight. Thanks to our simulations we know that if our theories of dark matter are correct then the Universe around us should be full of haloes that failed to make a galaxy. Perhaps astronomers will one day figure out a way to find them."

Gas in the EAGLE Simulation, showing hot bubbles (red colours) surrounding large galaxies, connected by colder filaments (blue and green colours). Inserts zoom in on the Local Group around the Milky Way and show the distribution of gas, stars and dark matter. Credit: Richard Bower, John Helly, Sarah Nixon, Till Sawala, James Trayford, Durham University

Lead researcher Dr Till Sawala, also at the Institute for Computational Cosmology at Durham University, said the research was the first to simulate the evolution of our 'Local Group' of galaxies, including the Milky Way, Andromeda, their satellites and several isolated small galaxies, in its entirety.

Dr Sawala said: "What we’ve seen in our simulations is a cosmic own goal. We already knew that the first generation of stars emitted intense radiation, heating intergalactic gas to temperatures hotter than the surface of the sun. After that, the gas is so hot that further star formation gets a lot more difficult, leaving haloes with little chance to form galaxies. We were able to show that the cosmic heating was not simply a lottery with a few lucky winners. Instead, it was a rigorous selection process and only haloes that grew fast enough were fit for galaxy formation."

The close-up look at the Local Group is part of the larger EAGLE project currently being undertaken by cosmologists at Durham University and the University of Leiden in the Netherlands. EAGLE is one of the first attempts to simulate – right from the start – the formation of galaxies in a representative volume of the Universe. By peering into the virtual Universe, the researchers find galaxies that look remarkably like our own, surrounded by countless dark matter haloes, only a small fraction of which contain galaxies.

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Science contacts

Dr Sawala and Prof. Frenk will be at the Royal Astronomical Society’s National Astronomy Meeting at the University of Portsmouth on Wednesday, June 25, and Thursday, June 26, 2014.

An ISDN radio line is available at the National Astronomy Meeting. To request its use please contact Sophie Hall at the University of Portsmouth on This email address is being protected from spambots. You need JavaScript enabled to view it.
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An ISDN radio line is also available at Durham University and bookings can be arranged via the Media Relations Team on the contact details above.

http://www.ras.org.uk/images/stories/NAM/2014/sawala_zoom.jpgGas in the EAGLE Simulation, showing hot bubbles (red colours) surrounding large galaxies, connected by colder filaments (blue and green colours). Inserts zoom in on the Local Group around the Milky Way and show the distribution of gas, stars and dark matter. Credit: Richard Bower, John Helly, Sarah Nixon, Till Sawala, James Trayford, Durham University

The work was funded by the UK's Science and Technology Facilities Council (STFC) and the European Research Council.

The Durham-led simulation was carried out on the “Cosmology Machine”, which is the part of the DiRAC national supercomputing facility for research in astrophysics and particle physics funded by the Department for Business, Innovation and Skills through the STFC. The Cosmology Machine – based at Durham University – has more than 5,000 times the computing power of typical PCs, and over 10,000 times the amount of memory.

The research is part of a programme being conducted by the Virgo Consortium for supercomputer simulations, an international collaboration led by Durham University with partners in the UK, Germany, Holland, China and Canada. The new results on the Local Group involve, in addition to Durham University researchers, collaborators in the Universities of Victoria (Canada), Leiden (Holland), Antwerp (Belgium) and the Max Planck Institute for Astrophysics (Germany).

Durham University is a world top-100 university with a global reputation and performance in research and education. The most recent UK league tables place Durham in the top echelon of British universities academically. Durham is ranked fifth in the UK in the Complete University Guide 2014 and sixth in the Times and Sunday Times Good University Guide 2014; it is 26th in the world for the impact of its research (THE citations ratings) and in the world top 25 for the employability of its students by blue-chip companies world-wide (QS World University Rankings 2013/14). It is a residential Collegiate University: England’s third oldest university and at its heart is a medieval UNESCO World Heritage Site, of which it is joint custodians with Durham Cathedral. Durham is a member of the Russell Group of leading research-intensive UK universities.

Set up in 2007 by the European Union, the European Research Council (ERC) aims to stimulate scientific excellence in Europe by encouraging competition for funding between the very best, creative researchers of any nationality and age based in Europe. Since its launch, the ERC has awarded grants to over 4,000 researchers performing frontier research in Europe. The ERC operates according to an "investigator-driven", or "bottom-up" approach, allowing both early-career and senior scientists to identify new opportunities in all fields of research (Physical Sciences and Engineering, Life Sciences and Social Sciences and Humanities), without predetermined priorities. The ERC has a total budget of €13.1 billion under Horizon 2020, the new EU research and innovation programme for 2014 - 2020.

The RAS National Astronomy Meeting (NAM 2014) will bring together more than 600 astronomers, space scientists and solar physicists for a conference running from 23 to 26 June in Portsmouth. NAM 2014, the largest regular professional astronomy event in the UK, will be held in conjunction with the UK Solar Physics (UKSP), Magnetosphere Ionosphere Solar-Terrestrial physics (MIST) and UK Cosmology (UKCosmo) meetings. The conference is principally sponsored by the Royal Astronomical Society (RAS), the Science and Technology Facilities Council (STFC) and the University of Portsmouth. Meeting arrangements and a full and up to date schedule of the scientific programme can be found on the official website and via Twitter.

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The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. Follow the RAS on Twitter.

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